To assign a frequency for new service or to assign a frequency to a new service provider was conventionally performed at the instigation of a government.
In particular, if there are new broadcasters, frequencies, that is, limited resources, were distributed by allocating a new frequency through auction, etc. or by recovering the existing frequency from the existing broadcaster and deploying the recovered frequency to another broadcaster.
With the recent spread of a variety of wireless Internet-based applications, such as open type terminal platforms, App stores, and mobile VoIPs, however, there is an explosive increase of the demands for radio data traffic. Accordingly, the distribution of frequencies that is led by a government as described above is very inefficient, and to secure a new frequency on the frequency distribution table basically became to gradually difficult.
In particular, with the rapid growth of broadcasting and communication systems, the next-generation communication system is designed in the convergence form of several networks, the system gradually becomes complicated, and a need for interoperability between systems is gradually expanded. Furthermore, as communication technology and service are developed, frequency of use for frequency resources is increased the shortage problem of a frequency has reached a critical situation because a specific frequency band is fixed occupied in order to provide excellent communication technology and service.
A frequency sharing method has been in the spotlight as a scheme capable of solving the problems. The frequency sharing method starts from a viewpoint that a current frequency shortage phenomenon results from the existing partition type frequency management method and a frequency seems to be short on the frequency distribution table, but the frequency shortage problem can be solved through a sharing method.
As the shortage problem of frequency resources is recognized as being important worldwide, the Federal Communications Commission (FCC) of U.S. has decided to apply cognitive radio technology, that is, frequency sharing technology, for TV idle frequencies (white space) and has amended related rules in order to increase spectrum usage efficiency and facilitate the introduction of new service on November, 2008.
This movement is gradually expanded. In 2009, England has permitted the use of frequency sharing technology based on Cognitive Radio (CR) in bands that are not spatially used in TV broadcasting bands, that is, the white space band. EU is now reviewing an introduction method. In Korea, a frequency sharing policy using the white space band is being prepared.
Cognitive radio technology refers to a system in which a communication apparatus by itself monitors a communication environment, determines and selects an operating method for optimal communication, and plans a future determination process from previous communication experiences. That is, the cognitive radio technology is technology for searching for idle resources (spectrum hole, white space) that are rarely utilized or not temporally/spatially used, from among frequency bands allocated to unlicensed bands, and use the retrieved idle resources adaptively and opportunistically. Here, when a primary user having a license to a corresponding band is detected, the use of the corresponding band is stopped or transmission power is controlled so that the primary user does not suffer from damage.
Meanwhile, to search for an idle frequency band as described above can be embodied more conveniently in homogeneous communication systems. It is however very difficult to search for an idle frequency band among heterogeneous communication systems, for example, heterogeneous communication systems, such as IEEE 802.16, WCDMA, or LTE, because the communication systems use different frequency bands. This is described with reference to FIG. 1.
FIG. 1 shows a difference between the frequency bands of radio systems.
As can be seen with reference to FIG. 1(a), a radio system A uses a wide frequency band and great power, whereas a radio system B uses a narrow frequency band and small power.
If the system B that operates in the illustrated narrow band uses f2, f5, and f8, there is a problem in that a frequency is not efficiently used because the system A that has to use a wider band cannot use any one of the bands f1 to f9.
Furthermore, as can be seen with reference to FIG. 1(b), a radio system C uses a very wide bandwidth and low power.
Accordingly, if the above-described radio systems A, B, and C are placed in the same area, the radio systems A, B, and C may interference with one another. Furthermore, assuming that the radio system B tries to use the frequencies f2, f5, and f8 as operating frequencies, the radio systems A and B interference with each other because the radio system A uses the frequencies f2, f5, and f8 as operating frequencies.
Furthermore, if the system C that operates in a wide bandwidth uses the band f5, the system B does not have an available band, resulting in deteriorated system efficiency.
As described above, it is very difficult for a specific system to search for a frequency band not used by another system because heterogeneous systems use different frequency bands. That is, there is a disadvantage in that it is difficult to efficiently distribute frequency resources if several systems having different bandwidths coexist.